1. Field of the Invention
The invention pertains to a hydraulic tension stop for vibration dampers, shock absorbers, or similar piston-cylinder assemblies of the type including a cylinder, a piston rod carrying a piston, and a piston rod guide. A liquid-filled working space is bounded axially by the piston rod guide and the piston, and radially by the cylinder and the piston rod, a part of the working space being assigned to the tension stop.
2. Description of the Related Art
A hydraulic tension stop for vibration dampers of this type is known from U.S. Pat. No. 4,901,828. For this purpose, an outwardly tensioned slotted damping ring is arranged with freedom of radial movement in a ring-shaped channel of a piston-like stop body. By way of a shallow conical section, which adjoins the cylindrical contact surface in the axial direction and extends with a taper toward the piston rod guide, the damping ring cooperates with pass-through openings, which lead across the ring-shaped channel, and thus changes the cross section of the openings. The damping ring is in contact with the outer contact surface at all times, that is, during any relative motion between the piston rod and the cylinder, and thus generates a frictional resistance, which prevents the damping effect from beginning gradually. In addition, as a result of the continuous contact between the damping ring and the contact surface, there is also the danger that particles can be rubbed off, which can impair the function of the damping devices.
Tension stops for hydraulic piston-cylinder assemblies are also known in which, after a predetermined excursion, a ring-shaped piston body attached to the piston rod travels into a damping cylinder designed to serve the tension damping function, the diameter of this cylinder being smaller than that of the main cylinder. To ensure that the tension damping functions satisfactorily even under the effect of transverse forces acting on the assembly, that is, even when the piston rod is pressed and bent against one side of the piston rod guide, the components which cooperate to provide the tension damping must be produced with very high precision, that is with extremely narrow tolerances, as a result of which these components are very expensive to produce.
The task of the present invention is to create a hydraulic tension stop with an axial damping travel which can be easily predetermined, where the tension stop is active only in the stop range, and where the damping effect and damping force curve can be easily adjusted to the requirements.
According to the invention, the tension stop includes a slide face which is permanently fixed to the cylinder in the working space, and a circumferential rest position channel in the slide face. A stop ring is mounted to the piston rod in the working space so that tension damping can be changed in a stroke-dependent manner, and a slotted outwardly tensioned damping ring cooperates with the stop ring. The damping ring is slideable against the slide face and seatable in the rest-position channel when the stop ring exceeds a predetermined position.
The desired axial damping travel and the point at which the tension stop starts to function are determined by the selection of the axial position of the rest-position channel in the working space. The rest-position channel makes it possible for the damping ring to be effective only in the end region assigned to the tension damping function. By way of the axial dimension of the conical surface and/or changes to the cross section of the slot in the damping ring, the open cross section and thus the damping force curve can be adjusted to the desired values. Additional bypass channels, as normally used in vibration dampers to change the damping force in certain positions of the damping piston, can also be used to change the open cross section during the hydraulic tension damping process.
The least possible friction between the damping ring and the slide face attached to the cylinder is obtained when the conical surface extends between the slide face and the base of the rest-position groove and when the damping ring has a beveled surface conforming to the conical surface. This arrangement makes it easier for the damping ring to be carried along when the tension damping process begins, and the abrasion between the damping ring and the slide face is minimized.
In a further elaboration of the invention, the slide face and the rest-position groove for the damping ring assigned to the tension damping function are located in a sleeve connected to the cylinder. This sleeve is pressed into the cylinder, for example, so that, to adapt the tension damping to a different set of damping requirements, only the sleeve needs to be replaced. There is no deed to replace the vibration damper with one of a different size.
To exclude undesired damping cross sections for the tension damping, it is advantageous to install a sealing disk between the stop ring and the damping ring; this sealing disk is easily held in position by a stop sleeve, which acts on the end surface of the disk. The stop sleeve also serves as a driver for the damping ring as the piston rod travels into the cylinder.
For this purpose, a driver surface and at least one pass-through opening are provided on the stop sleeve, so that, when the piston rod travels into the cylinder, the outward travel from the working space assigned to the tension damping function proceeds without any damping effect. So that the damping ring can be deposited in the rest-position channel, the driver surface on the stop sleeve is designed so that the connection with the piston rod is broken when the damping ring widens elastically.
A very wide range of freedom with respect to the choice of the open cross section is created according to the invention when the sleeve itself has a stroke-dependent open cross section. This stroke-dependent open cross section is created, for example, by means of at least one cutout in the sleeve, which tapers down in the lengthwise direction. The open cross section can also be created by several radial bores, which are arranged in a row in the axial direction in the sleeve and which open out into a pass-through channel, which is located between the inside wall of the cylinder and the sleeve and which preferably consists of a longitudinal groove in the sleeve on the side facing the cylinder.
If it is necessary to damp the operating noise of the hydraulic tension stop, a damping disk can be installed between the stop ring and the sealing disk. To improve the pressure relationships in the partial working space assigned to the hydraulic tension stop, the amount of oil present in the partial working space can be easily increased by expanding the cylinder in the area of the tension stop and by inserting an appropriately designed sleeve into this expanded area. This measure can also help to reduce the operating noise.
It is easy to combine the hydraulic tension stop with a mechanical tension stop known in and of itself. This can be done, for example, by installing the mechanical tension stop between the piston rod guide and the stop sleeve.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.